One of the most exciting developments in efforts to combat diabetes and its complications has been transplantation of healthy pancreatic tissue into diabetics. It is hoped that this approach will allow normalization of carbohydrate metablism with reduced risk of long term complications of the disease. Although promising results have been achieved by transplanting large numbers of isologous islets into diabetic animals, a corresponding approach to human therapy is hampered by the limited availabilityu of human islet tissue and the problems of immunological rejection. In preliminary experiments, we have observed the in vitro neogenesis of pancreatic islet-like structures (ILS's) following the culture of rat and human pancreatic tissue. These ILS's resembled pancreatic islets of Langerhans in their ability to synthesize and secrete insulin. Furthermore, the ILS's are capable of forming new generations of such structures following their subculture. Several pilot experiments were performed to determine whether diabetic rats would tolerate intraportal ILS grafts. We were encouraged by the observation that there was no lymphocytic infiltration around the transplanted ILS's for at least 4 days. There are two main objectives for the proposed investigation. The first is to extend our characterization of the ILS's in culture over several consecutive generations. This characterization will include measurements of proliferative capacity, rates of insulin synthesis and secretion, and an assessment of the ILS's responsiveness to physiologically significant stimuli such as glucose. The second aim is to evaluate the capacity of rat ILS's to reverse the diabetic state following their transplantation into diabetic rats. This will be correlated with the in vitro functional characteristics described above. Use of culture-derived islet-like structures for transplantation offers an abundant source of tissue plus the potential for reduced rejection problems. The importance of the proposed work, therefore, is that it provides the possibility overcoming these two major obstacles of therapeutic islet transplatation. Once a of viable method for islet transplantation is developed, with its advantages over conventional insulin replacement therapy, the diabetic patient may look forward to superior metabolic control, plus reduced long-term complications of his disease.